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3D mammograms detect more cancers

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According to the Los Angeles County Department of Public Health, breast cancer is the leading cause of premature death from cancer among women in the county. Many women undergo periodic mammograms with the goal of early detection and treatment. Despite the fact that mammograms are one of the best tools for breast cancer detection, the procedure has a number of limitations. One problem is the likelihood of a false-positive result, which causes emotional stress and unnecessary procedures such as biopsies and surgery. False-positive results are another problem; a mammogram read as normal will miss a cancer.

Now, an alternative exists that reduces the likelihood of the aforementioned problems: 3D mammography (tomosynthesis). Tomosynthesis is similar to conventional mammography in which the breast is compressed while an X-ray image is produced from the tissue. The difference is that the X-ray beam moves slightly over the woman’s head, taking multiple images, which are reconstructed by a computer into a 3D image. The result is a much more detailed representation of what the breast tissue looks like.

A new study published in the June 25 edition of the Journal of the American Medical Association (JAMA) reports that tomosynthesis can detect significantly more invasive cancers than the traditional mammogram. In addition, the procedure markedly reduced call-backs for women to undergo secondary imaging.

The study authors note that mammography plays an important role in early breast cancer detection. Numerous studies have reported that adding tomosynthesis to mammography increases cancer detection and decreases false-positive results. Therefore, they conducted a retrospective (backward-looking) study to assess whether mammography combined with tomosynthesis improves breast cancer screening the US. They reviewed the screening performance at 13 academic and nonacademic breast centers and subjected the data to statistical analysis.

The study comprised a total of 454,850 examinations (281,187 digital mammograms and 173,663 digital mammograms + tomosynthesis. The procedures were divided into two periods: (1) digital mammography screening examinations one year before tomosynthesis implementation (start dates ranged from March 2010 to October 2011 through the date of tomosynthesis use); (2) digital mammography plus tomosynthesis examinations from initiation of tomosynthesis screening (March 2011 to October 2012) through December 31, 2012. The main outcome measurements were: recall rate for additional imaging; cancer detection rate; and positive predictive values for recall and for biopsy.

The researchers found that with digital mammography, 29,726 women were recalled and 5,056 biopsies resulted in cancer diagnosis in 1,207 (815 invasive cancers and 392 in situ cancers (localized cancer that had not spread)). With digital mammography + tomosynthesis, 15,541 patients were recalled and 3,285 biopsies resulted in a breast cancer diagnosis in 950 patients (707 invasive and 243 in situ). Recall rates per 1,000 exams were: for recall rate, 107 with digital mammography vs. 91 with digital mammography + tomosynthesis (difference: –16); for biopsies, 18.1 with digital mammography vs. 19.3 with digital mammography + tomosynthesis (difference: 1.3); for cancer detection, 4.2 with digital mammography vs. 5.4 with digital mammography + tomosynthesis (difference: 1.2); and for invasive cancer detection, 2.9 with digital mammography vs. 4.1 with digital mammography + tomosynthesis (difference: 1.2). The in situ cancer detection rate was 1.4 per 1,000 screens with both methods. Adding tomosynthesis was associated with an increase in the positive predictive value for recall from 4.3% to 6.4% (difference: 2.1%) and for biopsy from 24.2% to 29.2% (difference: 5.0%).

The authors concluded that the addition of tomosynthesis to digital mammography was associated with a decrease in recall rate and an increase in cancer detection rate. They recommended that further studies should be conducted assess the relationship to clinical outcomes.

Take home message:

This study reports that 3D mammography (tomosynthesis) is superior for the detection of breast cancer and also reduces false-positive results. The only drawbacks to this procedure are a higher cost and increased radiation exposure.

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